The invention generally relates to pneumatically actuated liquid dispensing valves, such as those designed to dispense liquid hot melt adhesives. With increasing manufacturing line speeds it is important to improve the performance of these valves with respect to their ability to actuate quickly between on and off conditions. Traditionally, the fastest acting dispensing valves have been the more expensive electric guns.
Because air is a compressible fluid the actuating air volume in the actuation portion of the valve, and the actuation components coupled with the valve, plays a role in establishing the rate at which the dispensing valve may be switched between on and off conditions. An air supply device, such as an electrically operated solenoid valve, has been used to supply and switch the actuating air. When the solenoid is electrically activated to supply pressurized air to the liquid dispensing valve, the pressurized air acts against an actuator, such as a movable piston or diaphragm. This opens the liquid dispensing valve. The solenoid valve may be deactivated to then shut off or switch the pressurized air and allow a spring and/or pressurized air to close the liquid dispensing valve. The air volume in the outlet of the solenoid, the porting between the solenoid valve and the pneumatic actuator, and the air pathways and actuation portion of the dispensing valve itself, can provide an undesirable delay during the opening and closing of the valve due to the compressible nature of air.